Injector with adjustable dosing

ABSTRACT

An injector for injecting a medicament in a patient. The injector includes a container comprising a fluid chamber containing a first volume of a medicament, and an injection conduit associated with the fluid chamber for defining a fluid pathway therefrom to inject the medicament from the fluid chamber through the injection conduit to an injection location. The injector also includes a firing mechanism associated with the fluid chamber for expelling the medicament from the fluid chamber through the injection conduit, and a volume-control mechanism operable to control a fraction of the first volume of medicament that is injected when the firing mechanism is actuated to inject the medicament.

This application is a continuation of U.S. patent application Ser. No. 12/299,288 filed Jun. 3, 2009, which is a U.S. National Stage Entry of International Patent Application No.: PCT/US2007/068010 filed May 2, 2007, which in turn claims benefit of priority from U.S. Provisional Patent Application No.: 60/96,942 filed May 3, 2006. All patents, patent applications, and references cited anywhere in this specification are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to an injector, and more particularly to an injector with adjustable-dosing.

BACKGROUND OF THE PRESENT INVENTION

Injection devices for injection of medicaments into a patient are generally known. Such devices include, for example, traditional hypodermic needle syringes that contain a stock of medicament therein. Upon insertion of the needle wider the patient's skin at an injection location, the medicament is forced out of the syringe and through the needle by depression of a plunger mechanism.

Injection devices also include needle-free injectors, some of which are described in U.S. Pat. Nos. 5,599,302; 5,062,830; and 4,790,824; and needle-assisted injectors, such as those described in U.S. Patent Publication No. 2005/0033234. These jet injectors administer medicaments as a fine, high velocity jet delivered under sufficient pressure to enable the jet to pass through the skin, or for improved dispersion of the injected medicament. Self-injectors or autoinjectors like the ones disclosed in U.S. Pat. Nos. 4,553,962 and 4,378,015, and PCT Publications WO 95/29720 and WO 97/14455 are constructed to inject medicament at a rate and in a manner similar to hand-operated hypodermic syringes.

These injectors often are made for a single use, or alternatively to be refilled after each injection. Some refillable injectors can he refilled with a desired dosage to be injected. Upon injection, the entire loaded dosage is injected.

An injector is needed that can deliver a medicament into a patient in an adjustable dose that is equal to or less than the full amount contained in the injector.

SUMMARY OF THE INVENTION

The invention is related to an injector. A preferred embodiment of the injector includes a container comprising a fluid chamber containing a first volume of a medicament, and an injection conduit associated with the fluid chamber for defining a fluid pathway therefrom to inject the medicament from the fluid chamber through the injection conduit to an injection location. The injector also includes a firing mechanism associated with the fluid chamber for expelling the medicament from the fluid chamber through the injection conduit, and a volume-control mechanism operable to control a fraction of the first volume of medicament that is injected when the firing mechanism is actuated to inject the medicament.

Preferably, the volume-control mechanism is used to select a second volume, which is a portion or fraction of the first volume. The volume-control mechanism preferably includes a threaded ram that is biased by an energy source against a plunger and configured for rotating about a longitudinal axis of the injector. The volume-control mechanism also preferably includes a stopping member in threaded association with the ram and including at least one lateral member disposed within a track that extends longitudinally along a portion of the housing of the injector and is slidable therein. Preferably, the stopping member includes a pair of opposing lateral members, each disposed in separate opposing tracks. The lateral member prevents rotation of the stopping member about the longitudinal axis with the ram when the ram is rotated thereabout. The stopping member is configured for limiting movement of the ram along the longitudinal axis, the position of the stopping member being adjustable along the longitudinal axis with respect to the ram. The volume-control mechanism also includes a cap associated, and preferably removeably engageable, with the ram and configured for rotating the ram about the longitudinal axis to select an injection volume such that when the ram is rotated, the position of the stopping member is adjusted along the longitudinal axis with respect to the rain. Upon actuation of the energy source, which is preferably a spring, biasing of the ram against the plunger is preferably limited when the lateral member abuts the distal end of the track.

In one embodiment, the housing includes a transparent window adjacent the length of the track such that the longitudinal position of the stopping member within the injector is visible through the window. Preferably, the transparent window includes indicia corresponding to the position of the stopping member and the selected injection volume.

Preferably, the injector also includes a bearing member, such as an annular bushing or other bearing, disposed between the energy source and the ram, and configured for preventing or substantially reducing friction therebetween when the ram is rotated. The injector is preferably configured for single-use injection of medicament therefrom. Alternatively, the injector is configured for multiple injections of medicament therefrom.

In the preferred embodiment, the container is a prefilled syringe, and further includes an injection-assisting needle disposed in fluid communication with the fluid chamber, the needle having an injecting tip configured for piercing the patient's skin at the injection location. The housing houses the prefilled syringe and is configured for allowing insertion of the needle at the injection location to an insertion point that is at a penetration depth below the patient's skin. The injector preferably includes a syringe support supportively mounting the prefilled syringe to the housing. In other embodiments, the container is a needle-free cartridge, or a cartridge comprising an injection-assisting needle associated therewith.

In the preferred embodiment, the housing includes a retractable guard that is movable between a protecting position, in which the injection conduit is disposed within the guard, and an injecting position, in which the tip of the injection conduit is exposed for injection of the medicament at the injection location. A trigger mechanism is preferably operably associated with the energy source for actuation of the energy source to inject the medicament. Preferably, the trigger mechanism is configured for actuation of the energy source after the retractable guard is retracted from the protecting position. The retractable guard is preferably operably associated with the trigger mechanism to cause the trigger mechanism to activate the energy source when the guard is retracted to the injecting position.

The present invention thus provides an injector that enables a user to control or adjust the dose of medicament that is intended to be delivered to the patient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a preferred embodiment of an injector constructed according to the present invention, showing the injector prior to injection;

FIG. 2 is a cross-sectional view thereof, taken from a viewing perspective that is rotated 90° about the longitudinal axis of the injector front the perspective of FIG. 1; and

FIG. 3 is a perspective view of another embodiment of an injector.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a preferred embodiment of an injector 10 has an outer housing 12, defined between a proximal end 6 and a distal end 8, and configured for allowing a user, typically the patient him or herself, to handle the injector 10 and position the injector near or adjacent an injection location. The outer housing 12 preferably houses most of the components of the injector 10. The injector 10 also includes a cover member 14 configured to associate with the outer housing 12 and cover the distal end of the injector 10 prior to use. A container support member 16 is housed within and mourned with the housing 12. The container support member 16 is configured to hold and position a container 18 within the injector 10. The container 18 can be, for example, a cartridge, syringe, or any other suitable container for holding medicament therein. In the preferred embodiment shown in FIG. 1, the container is a prefilled syringe 18. Alternatively, instead of a prefilled syringe attached to a needle, the syringe can have a separate needle that is associated and brought into fluid communication with the medicament container prior to or upon firing of the injector. In the preferred embodiment, the container support member 16 is substantially fixed to the outer housing 12, such as by snaps, an adhesive, a weld, or another known attachment. The container 18 has a container portion 20 that defines in its interior a fluid chamber 22, which is preferably prefilled with medicament to be injected. In another embodiment, however, this chamber can initially be provided empty.

At the distal end of the container 18 is an injection-assisting needle 24, which is in fluid communication with an injection port 25 of the fluid chamber 22. Needle 24 has an injecting tip 26 configured as known in the art to penetrate the tissue of a patient, preferably the skin, at the injection location. A needle bore extends through the needle 24, as known in the art. The bore is in fluid communication with the injection port 25 and the medicament in the fluid chamber 22, and is open at the needle tip 26 to inject the medicament.

In needle-free injector embodiments, the container does not include a needle and the injection port of the fluid chamber preferably defines a fluid pathway in fluid communication with the fluid chamber for injecting medicament as a jet from the chamber through the port to the injection location. An example of a suitable needle-free jet nozzle arrangement is disclosed in U.S. Pat. No. 6,309,371.

At a proximal side of the fluid chamber 22, opposite from the needle 24, is a plunger 28 that preferably seals the medicament in the fluid chamber 22. A container wall 30 preferably comprises a tubular portion, preferably closed at a distal end and open at a proximal end, to define the fluid chamber 22. Plunger 28 is slideably received in the tubular portion. The container 18 is configured such that when the plunger 28 is displaced in a distal direction, the volume of the fluid chamber 22 is decreased, forcing the medicament out therefrom and through the injection port 25 and the bore of needle 24.

At the distal end of the fluid chamber 22 is a needle hub portion 32 to which the needle is mounted. A container flange 34 extends radially, preferably from the proximal end of the container wall 30.

In the preferred embodiment, the container 18 has a container body 36 that includes the flange 34, wall 30, and hub portion 32 of unitary construction. A preferred material for the container body 36 is glass, but other materials can be used in other embodiments. For example, a suitable prefilled syringe is the BD Hypak™, which is available in various sizes and volumes and is sold prefilled with medicament. The glass of the syringe body is adhered to the needle. Typical medicaments and medicament categories include epinephrine, atropine, sumatriptan, antibiotics, antidepressants, and anticoagulants.

In some embodiments, the injector includes a container cushion configured for providing additional support to the container within the housing, such as disclosed in International Application No. PCT/US2006/0002429, now WO 2006/079064. The container cushion 38 is preferably made of an elastomeric material or other resilient material. A flange of the container cushion 38 extends radially and is disposed and serves as an interface between the distal side of the container support member 16 and the container flange 34. Elevated portions, such as nubs, preferably extend proximately from the cushion flange and are configured and dimensioned to abut the container flange 34. A sleeve portion of the container cushion 38 extends axially around the interior of the container support 16. The container cushion 38 is preferably received in the interior of the container support 16 and receives the container body 36, preferably fitting snugly therein.

Referring to FIGS. 1 and 2, trigger mechanism 52 is preferably also housed within outer housing 12. The trigger mechanism 52 includes an inner member, such as an inner housing 54, that can be attached to the outer housing 12, such as by snaps, an adhesive, a weld, or other known attachment. Trigger protrusions 56 extend inwardly from the proximal end of the inner housing 54 and are normally resiliently biased outwardly. Trigger protrusions 56 are received in a recess 58 of firing ram 60 in blocking association therewith. The trigger protrusions 56 prevent distal movement of the ram 60 prior to the firing of the injector 10 upon actuation of the trigger mechanism 52. The rain 60 is urged towards the distal end of the injector 10 by an energy source, which preferably is a compression spring 62, although other suitable energy sources can alternative be used such as elastomer or compressed-gas springs, or gas generators. A preferred type of compression spring is a coil spring.

A trigger member of the trigger mechanism 52, such as a latch housing 64, is provided exterior to the inner housing 54 to retain the trigger protrusions 56 in the blocking association in the recess 58 to prevent premature firing of the injector 10. The latch housing 64 is slideable inside the outer housing 12 with respect to the inner housing 54, preferably in an axial direction, and the latch housing 64 preferably surrounds the inner housing 54.

The distal end of the outer housing 12 preferably includes a needle guard 66 that is moveable with respect to the outer housing 12. The needle guard 66 is shown in FIG. 2 in a protecting position, in which the needle 24 is disposed within the guard 66. The needle guard 66 is retractable, preferably into the outer housing 12, in a proximal direction to an injecting position, in which the needle tip 26 and an end portion of the needle 24 is exposed for insertion into a patient. In the preferred embodiment, the proximal movement of the guard is substantially prevented at the injecting position. In embodiments where the container does not include a needle, the injection port and the distal end of the fluid chamber can be exposed upon retraction of the needle guard to the injecting position.

The needle guard 66 is associated with the latch housing 64 such that when the guard 66 is displaced distally it slides the latch housing 64 also in a distal direction to release the trigger protrusions 56 from the recess 58. Preferably, the latch housing 64 has a latching portion that abuts the inner housing 54 in an association to bias and maintain the trigger protrusions 56 positioned in the blocking association with the ram 60 prior to the firing of the injector 10. When the latch housing 64 is slid proximately by the retracting of the guard 66 to the injecting position, the latching portion slides beyond the portion of inner housing 54 that it contacts, allowing the trigger protrusions 56 to move radially outwardly from the recess 58 and therefore from the blocking association. When this happens, i.e., when the trigger mechanism 52 is actuated, the spring 62 biases the ram 60 against plunger 28 to fire the injector 10. Latch housing 64 preferably defines trigger openings 70 adjacent to the latching portions, which are configured to receive a portion of the inner housing 54, such as the surface disposed radially outwardly from the trigger protrusions 56.

The guard 66 is preferably resiliently biased distally towards the protecting position by compression coil spring 72, or other biasing member. Also, the needle guard 66 has an axial opening 74 to allow the needle 24 pass therethrough, and which may be sized according to the type of injector desired. In embodiments of the injector that do not include a needle, the axial opening can be sized to allow the distal end of the fluid chamber and injection port to pass therethrough. The construction of the embodiment of FIG. 2 allows a user to push the distal end of the injector 10 against the patient's skin, pushing the needle 24 into the skin at an injection location, substantially at the same speed as the injector is pushed. Once the needle 24 is fully inserted to an insertion point at a penetration depth, the trigger mechanism 52 fires the injection of medicament into an injection location.

Other embodiments can incorporate alternative trigger mechanisms for actuating firing of the injector. For example, the injector can include a button or other suitable depressible member on the outer housing that, upon depression thereof, actuates firing of the injector.

Preferably, the injecting position of the guard 66 is such that a predetermined length of the end of needle 24 is exposed from the guard 66. In some embodiments, such as where the opening 74 is of a sufficiently large diameter, the skin of the patient maybe allowed to extend into the opening 74 when the device 10 is pressed there against, and a needle or injection port that does not protrude beyond the distal end of the guard 66 can be used. Some embodiments have a guard with a distal, skin-contacting surface that is discontinuous. In most embodiments where the injector includes a needle, the distance by which the needle tip extends past the distal end of the guard will be fairly close to the depth of the insertion of the needle.

In the preferred embodiment, such as for subcutaneous injection, the guard 66 is configured to allow insertion of the needle to a penetration depth in the skin that is up to about 5 mm below the skin surface. More preferably, the penetration depth is less than about 4 mm, and in one embodiment is less than about 3 mm. Preferably, the insertion depth is at least about 0.5 mm and more preferably at least about 1 mm. In another embodiment, the distance by which the needle extends past the guard 66 or the distal surface of the guard 66 that contacts the skin is up to about 5 mm, more preferably up to about 4 mm, and in one embodiment up to about 3 mm. Preferably, extension distance is at least about 0.5 mm, more preferably at least about 1 mm, and most preferably at least about 2 mm. In a preferred embodiment, tip 26 extends by a distance of around 2.5 mm beyond the portion of the guard 66 that contacts the skin in the injecting position.

In another embodiment, such as for intramuscular injection, the injector is configured to allow the needle to be inserted into the patient to a penetration depth in the skin, or alternatively beyond the distal surface of the guard, by a distance of up to about 15 mm. In one embodiment, this distance is about between 10 mm and 14 mm. In an embodiment for jet injection of epinephrine for instance, a preferred penetration depth or distance beyond the guard is between about 12 mm and 13.5 mm, and most preferably around 12.7 mm. Jet injection with this length needle improves the distribution of the medicament in the patient tissue compared to non-jet injection. Other exposed needle lengths can be selected for jet injection to different depths below the skin, with a preferred overall penetration length of between about 0.5 nun and about 20 mm. In these embodiments, the needle guard is preferably configured for retracting from a protecting position, preferably covering the entire needle, to an injecting position, in which the desired length of the end of the needle is exposed. In alternative embodiments, the needle tip stops behind or proximal to the guard, and penetrates the skin that is pushed into the guard.

In sonic embodiments, the energy source, which is preferably spring 62, and the container, which is preferably prefilled syringe 18, are configured to jet inject the medicament into the patient to an injection site. The spring 62 applies a force on the plunger 28 that is preferably sufficient to elevate the pressure within the fluid chamber 22 to a level high enough to eject the medicament from the needle 24 as a jet. Jet injection is to be understood as an injection with sufficient velocity and force to drive the medicament to locations remote from the needle tip 26 or injection port 25. The jet injector embodiments deliver a jet injection, the medicament is jet injected distally or in other directions, such as generally radially by the elevated pressure jet, which beneficially improves the distribution of the medicament after the injection and keeps a large bolus from forming that can detrimentally force the medicament to leak back out of the patient around the needle or through the hole left behind by the needle after it is removed. In alternative autoinjector embodiments that use needles, the injection pressures are relatively very low, and the medicament exits the needle tip inside the patient and is typically deposited locally around the needle in a bolus,

Preferably, in embodiments where needles are used, the needles are between 26 and 28 gage, and are most preferably around 27 gage, but alternatively other needle gages can be used where the other components are cooperatively configured to produce the desired injection. Preferably, the components of the injector 10 are configured to jet inject the medicament to a subterraneous injection site.

Preferred injection rates are below about 0.75 mL/sec., more preferably below about 0.6 mL/sec., and preferably at least about 0.2 mL/sec., more preferably at least about 0.3 mL/sec, and most preferably at least about 0.4 mL/sec. Preferably, the injection of the entire amount of medicament is completed in less than about 4 seconds, more preferably in less than about 3 seconds, and most preferably in less than about 2.5 seconds. Preferably, the medicament injection takes at least about 1 second, and inure preferably at least 1.5 seconds, and most preferably at least about 1.75 seconds. A preferred embodiment injects the medicament at about 0.5 mL/sec., completing the injection of 1 mL in about 2 seconds. Other alternative injection rates, injection volumes, and injections times can also be used.

The entire amount of medicament contained and injected from fluid chamber of the container is preferably between about 0.02 mL and 4 mL, and preferably less than about 3 mL, and in the preferred embodiment is around 1 mL. Larger volumes may also be selected depending on the particular medicament and dosage required. Preferably, the container 18 shown in FIG. 1 is assembled into the remaining parts of the injector 10 already containing the desired amount of medicament. In a preferred embodiment, the container 18 contains about 1 mL of medicament.

As shown in the preferred embodiment of FIG. 1, the injector 10 includes a volume-control mechanism 90 configured to select the fraction of medicament in the fluid chamber 22 that is to be injected, or correspondingly the dosage volume to be injected. The volume-control mechanism of this embodiment includes the ram 60, a cap 82, and a stopping member 100.

The ram 60, as previously described, preferably has a threaded portion 61 and is configured for rotating about its longitudinal axis 110 to permit the option of injecting less than all of the medicament. Stopping member 100 preferably includes a body portion 102, which can be configured as an internally threaded nut, and at least one lateral wing, and preferably two lateral wings 104 extending laterally, and preferably on opposing sides of the body portion 102. The body portion 102 is preferably in threaded association with the ram 60 and is longitudinally moveable therealong. Each of the lateral wings 104 is preferably disposed and slideable within respective tracks 106 that extend longitudinally. Tracks 106 are preferably associated with or are defined in the outer housing 12, and are positioned in the embodiment shown on opposite lateral sides of the outer housing 12. Each of the tracks 106 preferably has a proximal end 107 and a distal end 108, which define a track length therebetween. Upon rotation of the ram 60, tracks 106 prevent rotation of the lateral wings 104 about the longitudinal axis 110. Consequently, the position of the body portion 102 moves or is adjusted proximally or distally longitudinally along the threaded portion 61 of the ram 60, the lateral wings 104 sliding in the tracks 106 therewith. In the preferred embodiment, the distal end 108 of the track 106 acts as to blocking member and prevents distal movement of the stopping member 100, and enlarged portion 101 of the ram 60 prevents proximal movement thereof, but other structures can alternatively be used for this purpose.

By rotating the ram 60, the stopping member 100 is positioned to limit the throw of the ram 60 when the injector 10 is fired, allowing the selection of volume of medicament to be injected from the fluid chamber 22. Upon actuation of the spring 62 by the trigger mechanism 52, the ram 60 is biased distally against the plunger 28, thus displacing plunger 28 in a distal direction to force medicament out of the fluid chamber 22. Movement of the ram 60 distally against the plunger 28, and thus the volume of medicament that is injected from the fluid chamber 22 (i.e., the injection volume), is limited by the lateral wings 104 of the stopping member 100. For example, the ram 60 can only move distally upon actuation of the spring 62 until the lateral wings 104 are stopped by the distal ends 108 of the tracks 106. At that point, further movement of the ram 60 in the distal direction is prevented. The position of the stopping member 100 along the ram 60 thus effectively controls the injection volume of medicament injected from the fluid chamber 22.

The operable member for rotating the ram 60 about the longitudinal axis 110 to adjust the longitudinal position of the stopping member 100 is preferably cap 82 that is preferably removeably engageable with the ram 60. The cap 82 preferably includes an engagement portion 83 configured for mating receipt within a receiving portion 84 of the ram 60. In this configuration, twisting or rotation of the cap 82 while the engagement portion 83 is received in the receiving portion 84 results in rotation of the ram 60 about the longitudinal axis 110. By manipulating the cap 82, the position of the stopping member 100 can be adjusted proximately or distally along the ram 60 to select the fraction of medicament that is desired to be injected from the fluid chamber 22. The engagement and receiving portions 83,84 are preferably non-circular to prevent or restrict axial rotation therebetween.

In the preferred embodiment, for example, the length of the tracks 106 is substantially equal to the length between the distal end 109 of the fluid chamber 22 and the distal end of the plunger 28. Thus, when cap 82 is twisted to position the stopping member 100 in its most proximal position along the ram 60 (i.e., with the lateral wings 104 disposed against the proximal ends 107 of the tracks 106), actuation of the spring 62 causes the rain 60 to move distally against the plunger 28 as the lateral wings 104 slide along the entire length of track 106 before abutting the distal ends 108 of the tracks, and the plunger 28 correspondingly is moved distally through the fluid chamber 22 to the distal end 109 thereof, injecting the entire volume of medicament therefrom.

If the cap 82 is twisted to position the stopping member 100 more distally along the ram 60, then the injection volume will only be a fraction of the entire volume of medicament in the fluid chamber 22 because upon actuation, the lateral wings 104 will slide along the tracks 106 and abut the distal ends 108 thereof to prevent the ram 60 from biasing the plunger 28 completely to the distal end 109 of the fluid chamber 22. As such, the entire volume of the medicament in the fluid chamber 22 is not injected. One of ordinary skill iii the art would understand that the cap 82 can be twisted to adjust the position of the stopping member 100 relative to the ram 60 to select the appropriate injection volume of medicament that is desired to be injected.

Alternative embodiments can be provided with different throw and adjustment ranges to limit the range of adjustability to less than from 100% to 0% of the total volume of contained medicament. In one embodiment, the upper limit of volume fraction is less than 100%, e.g., about 90% or about 80%, and the lower limit is more than 0%, e.g., about 10%, 30%, or 50%. Additionally, other embodiments of the injector can include alternative mechanisms that are configured to limit the throw/adjustment ranges or the volume of medicament ejected from the injector.

Preferably, the outer housing 12 includes a window portion 110 adjacent the tracks 106 and along the length thereof, as shown in the preferred embodiment of FIG. 4. The window portion 110 is preferably made of a hard and durable, yet substantially transparent, material to allow the position of the lateral wings 104 of stopping member 100 to be visible therethrough. More preferably, the window portion 110 includes indicia 112 along and adjacent the length of the tracks that corresponds to the injection volume to be injected from the fluid chamber 22. For example, the indicia can include marking intervals between 0% to 100% (the 0% marking disposed adjacent the distal end 108 of the track and the 100% marking disposed adjacent the proximal end 107 of the track) such that adjusting the position of the stopping member 100 so that the lateral wings 104 are substantially aligned with a 75% marking indicates that the injection volume will be 75% of the entire volume of medicament contained in the fluid chamber 22.

One of ordinary skill the art would understand that other such indicia or marking schemes can be used as desired. For example, indicia can be included on the housing adjacent the window rather than directly on the window, or the indicia can correspond to absolute values of injection volumes rather than percentages of the entire volume of medicament in the fluid chamber.

The preferred embodiment of the injector 10 shown in FIG. 1 also includes a bearing disposed between the spring 62 and the rain 60. The bearing is preferably an annular bushing 68, such as a nylon washer. The bushing 68 is configured for preventing or substantially reducing friction between the spring 62 and the ram 60 as the ram is rotated about the longitudinal axis 110, while still transferring biasing energy from the spring 62 to the ram 60 upon actuation of the spring.

While the preferred embodiments disclosed herein have been described in terms of a single-use injector (i.e., where a single injection volume of medicament is injected from a container prior to replacing the used container with a new container), one of ordinary skill in the art would understand that in other embodiments of the present invention, multiple injection volumes can be injected from the same container. For example, a first injection volume of 80% of the entire volume of medicament in the fluid chamber may be injected, followed by a subsequent injection of a second injection volume of the same or different fraction of the remaining volume of medicament in the fluid chamber.

The preferred embodiment is a single-use injector, being configured to prevent a user from reloading and reusing the injector. As such, the embodiment of FIG. 1 does not have a way of resetting the injector to fire again, and preferably cannot be reloaded to with another medicament container without substantial disassembly or breaking of the injector. An alternative embodiment, however, is a reusable injector that can be reset, such as by reloading the firing mechanism and reloading the medicament.

The content of International Application No. PCT/US2006/0002429, now WO 2006/079064, is hereby expressly incorporated herein by reference thereto. The term “about,” as used herein, should generally be understood to refer to both the corresponding number and a range of numbers. Moreover, all numerical ranges herein should be understood to include each whole integer within the range.

While illustrative embodiments of the invention are disclosed herein, it will be appreciated that numerous modifications and other embodiments may be devised by those skilled in the art. For example, the features for the various embodiments can be used in other embodiments. Therefore, it will be understood that the appended claims are intended to cover all such modifications and embodiments that come within the spirit and scope of the present invention. 

What is claimed is:
 1. An injection device for injecting medicament in a patient comprising: a fluid chamber configured to contain a medicament; a housing configured to house the fluid chamber; an injection conduit associated with the fluid chamber for defining a fluid pathway from the fluid chamber to the patient; a firing mechanism associated with the fluid chamber and configured to be actuated to expel the medicament from the fluid chamber through the injection conduit, the firing mechanism comprising: a ram configured to move with respect to the fluid chamber, thereby dispelling medicament from the fluid chamber, wherein the ram is threaded and is positioned along a longitudinal axis of the injection device; a trigger having protrusions biased outwardly and in blocking association with the ram in a protecting position; and a latch housing configured to retain the trigger protrusions in blocking association with the ram in the protecting position and allow the trigger protrusions to disengage from the ram in an injection position; and a volume control mechanism configured to be adjusted to select a volume of the medicament from the fluid chamber that is injected from the injection conduit when the firing mechanism is actuated, wherein the volume control mechanism includes a stopping member rotatably coupled to the ram and a user engageable control removably coupled to the ram to rotate the ram about the longitudinal axis to select the volume of the medicament to be injected by selectively adjusting the position of the stopping member relative to the ram, wherein adjusting the position of the stopping member includes repositioning the stopping member longitudinally along the ram.
 2. The injection device of claim 1, wherein the ram is configured to be biased toward a distal end of the injection device when the firing mechanism is actuated; wherein the trigger protrusions are resiliently biased outwardly relative to the longitudinal axis of the injection device, wherein the injection conduit is disposed within a retractable guard when the ram is in the protecting position; and wherein the latch housing-is configured to move relative to the trigger protrusions to allow the trigger protrusions to move radially outwardly from the blocking association with the ram in the injection position in which a tip of the injection conduit is exposed for injection of the medicament at an injection location.
 3. The injection device of claim 2, wherein the retractable guard is positioned at a distal end of the injection device, the retractable guard being moveable between an extended position and a retracted position, wherein the retractable guard is associated with the latch housing such that movement of the retractable guard is configured to slide the latch housing proximately to allow the trigger protrusions to move radially outwardly from the blocking association with the ram, thereby allowing the ram to move with respect to the fluid chamber.
 4. The injection device of claim 3, wherein the stopping member is in threaded association with the threaded ram, wherein the ram is rotatable with respect to the stopping member for selectively positioning the stopping member longitudinally along the ram to select the volume of the medicament to be expelled from the fluid chamber, and the volume control mechanism further includes a blocking portion positioned to block distal movement of the stopping member associated with the ram when the firing mechanism is actuated to expel the medicament.
 5. The injection device of claim 4, wherein the stopping member comprises at least one lateral extension that protrudes laterally from the ram and is configured to be longitudinally aligned with the blocking portion.
 6. The injection device of claim 5, wherein the volume control mechanism defines a track that extends generally longitudinally, the lateral extension being slidably received therein, wherein the at least one lateral extension is configured to prevent rotation of the stopping member when the ram is rotated.
 7. The injection device of claim 6, wherein the housing defines the track, and wherein the track has a distal end that comprises the blocking member.
 8. The injection device of claim 7, wherein the housing includes: a window adjacent the length of the track such that the longitudinal position of the stopping member within the injection device is visible through the window; and indicia adjacent the window for determining the volume of the medicament to be injected.
 9. The injection device of claim 2, wherein the firing mechanism further comprises an energy source activatable for expelling the medicament.
 10. The injection device of claim 9, wherein the injection conduit comprises an injection-assisting needle.
 11. The injection device of claim 9, further comprising a bearing member disposed between the energy source and the ram and configured for reducing friction therebetween when the ram is rotated.
 12. The injection device of claim 4, wherein the firing mechanism further comprises an energy source activatable for expelling the medicament, and the ram is operably associated with the energy source such that the ram is biased by the energy source when the firing mechanism is activated.
 13. The injection device of claim 1, wherein the user engagable control is configured to disengage from the ram when the firing mechanism is actuated.
 14. The injection device of claim 13, wherein the user engagable control includes a cap coupled to the housing and a coupling rotationally fixed relative to the ram and is configured to rotate the ram when the cap is rotated, and wherein the coupling is configured to disengage from the ram when the ram is driven away from the coupling upon activation of the firing mechanism.
 15. The injection device of claim 1, wherein the user engageable control is engageable by a user while the device is fully assembled.
 16. The injection device of claim 15, wherein the user engageable control is configured to be manually moved to rotate the ram.
 17. The injection device of claim 1, wherein the fluid chamber comprises a prefilled syringe, and the injection device further comprises an injection-assisting needle disposed in fluid communication with the fluid chamber, the injection-assisting needle having an injecting tip configured for piercing the patient's skin at an injection location.
 18. The injection device of claim 1, further comprising a retractable guard disposed at a distal end of the injection device and movable from a needle guard extended position to a needle guard injecting position for activating the firing mechanism. 